Aqueous emulsion polymerization in the presence of ethers as chain transfer agents to produce fluoropolymers

ABSTRACT

The present invention provides a method of making a fluoropolymer comprising repeating units derived from one or more gaseous fluorinated monomers. The method comprises an aqueous emulsion polymerization of gaseous fluorinated monomers in the presence of an ether selected from the group consisting of dimethyl ether (DME), methyl tertiary butyl ether (MTBE) and mixtures thereof.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 60/288,248, filed May 2, 2001.

FIELD OF THE INVENTION

The present invention relates to an improvement of the aqueous emulsionpolymerization for making fluoropolymers. In particular, the presentinvention relates to the use of particular ethers as chain transferagents in the aqueous emulsion polymerization for making fluoropolymerswith improved properties, in particular fluorothermoplasts andfluoroelastomers with improved properties.

BACKGROUND OF THE INVENTION

Fluoropolymers, i.e. polymers having a fluorinated backbone, have beenlong known and have been used in a variety of applications because ofseveral desirable properties such as heat resistance, chemicalresistance, weatherability, UV-stability etc . . . The variousapplications of fluoropolymers are for example described in “ModernFluoropolymers”, edited by John Scheirs, Wiley Science 1997.

The known fluoropolymers include in particular fluoroelastomers andfluorothermoplasts. Such fluoropolymers include copolymers of a gaseousfluorinated olefin such as tetrafluoroethylene (TFE),chlorotrifluoroethylene (CTFE) and/or vinylidene fluoride (VDF) with oneor more comonomers such as for example hexafluoropropylene (HFP) orperfluorovinyl ethers (PVE) or non-fluorinated olefins such as ethylene(E) and propylene (P). The term “copolymer” in connection with thepresent invention should generally be understood to mean a polymercomprising repeating units derived from the recited monomers withoutexcluding the option of other further repeating units being present thatderive from other monomers not explicitly recited. Accordingly, forexample the term ‘copolymer of monomers A and B’ includes binarypolymers of A and B as well as polymers that have further monomers otherthan A and B such as for example terpolymers.

Examples of fluoroelastomers include for example copolymers of TFE andPVE and copolymers of VDF and HFP. The fluoroelastomers may also containcure site components so that they may be cured if desired. Applicationsof fluoroelastomers include for example coatings, use as gaskets andseals as well as use as polymer processing aids (PPA). A commerciallyavailable processing aid includes for example copolymers of VDF and HFPavailable from Dyneon LLC under the brand DYNAMAR™ PPA.

Examples of fluorothermoplasts include copolymers of TFE and E (ETFE),copolymers of TFE and HFP (FEP), copolymers of TFE, HFP and VDF (THV)and perfluoroalkoxy copolymers (PFA). Examples of applications offluorothermoplasts include for example coating applications such as forexample for coating outdoor fabric and use as insulating material inwire and cable insulation. In particular ETFE copolymers have desirableproperties as insulating material. Further applications offluorothermoplasts include making of tubes such as for example fuelhoses, extrusion of films and injection molded articles. The extrudedfluorothermoplastic articles, in particular films may further besubjected to an e-beam radiation to partially cure thefluorothermoplast.

Several methods are known to produce the fluoropolymers. Such methodsinclude suspension polymerization as disclosed in e.g. U.S. Pat. Nos.3,855,191, 4,439,385 and EP 649863; aqueous emulsion polymerization asdisclosed in e.g. U.S. Pat. Nos. 3,635,926 and 4,262,101; solutionpolymerization as disclosed in U.S. Pat. Nos. 3,642,742, 4,588,796 and5,663,255; polymerization using supercritical CO₂ as disclosed in JP46011031 and EP 964009 and polymerization in the gas phase as disclosedin U.S. Pat. Nos. 4,861,845.

Currently, the most commonly employed polymerization methods includesuspension polymerization and especially aqueous emulsionpolymerization. Aqueous emulsion polymerization has been generallypreferred for the production of fluoropolymers because the process ismore environmental friendly than solution polymerization in organicsolvents and furthermore allows for easy recovery of the resultingpolymer. However, for certain applications, the fluoropolymers producedvia the aqueous emulsion polymerization process may have somewhatinferior properties relative to similar polymers produced via solutionpolymerization. For example, copolymers of E and TFE produced accordingto the solution polymerization disclosed in U.S. Pat. Nos. 4,123,602generally have a better heat resistance than similar polymers producedvia aqueous emulsion polymerization.

The aqueous emulsion polymerization normally involves the polymerizationin the presence of a fluorinated surfactant, which is generally used toensure the stabilisation of the polymer particles formed. The suspensionpolymerization generally does not involve the use of surfactant butresults in substantially larger polymer particles than in case of theaqueous emulsion polymerization. Thus, the polymer particles in case ofsuspension polymerization will quickly settle out whereas in case ofdispersions obtained in emulsion polymerization generally display goodlatex stability over a long period of time.

Although the aqueous emulsion polymerization generally involves the useof a fluorinated surfactant, there is also known an aqueous emulsionpolymerization process wherein no fluorinated surfactant is added to thepolymerization system. Such a polymerization is described in for exampleU.S. Pat. Nos. 5,453,477 and WO 97/17381. It is taught therein thatthrough careful selection of the initiation system, the polymerparticles are self-stabilized through the ionic endgroups of thepolymers produced in the process.

To tailor the molecular weight of the resulting fluoropolymer, it hasbeen known to use chain transfer agents. For example, U.S. Pat. Nos.4,766,190 discloses an aqueous emulsion polymerization to makefluoroelastomers. The chain transfer agents disclosed include C₄-C₆hydrocarbons, alcohols, ethers, esters, ketones and halocarbons.

U.S. Pat. No. 4,262,101 also discloses an aqueous emulsionpolymerization process. Chain transfer agents used here includehalocarbons, aliphatic carboxylic acid esters, ketones, alcohols,malonic esters and lower dialkylglycol.

U.S. Pat. No. 5,608,022 discloses the preparation of a copolymer of TFEand a comonomer of the formula CF₂═CF—O—(CF₂CF(CF₃)—O)_(n)—(CF₂)_(m)—Zwherein n is 1 or 2, m is 2-4 and Z is CO₂R or SO₂F with R being C₁-C₃alkyl. The polymerization is carried out by dispersing the comonomer inwater to a droplet size of less than 2 μm and copolymerizing with TFE inthe presence of a C₁-C₆ alcohol or a C₂-C₆ ether. The alcohols are beingdisclosed as the preferred chain transfer agent and the chain transferagents are being mixed as liquid with the aqueous polymerization medium.It is disclosed that the copolymer can be produced avoiding formation ofdifferent kind of polymers in the aqueous medium, in particular theformation of homopolymer of TFE is avoided. In the examples, n-propylether is used as a chain transfer agent. However ethers such as n-propylether and diethyl ether have been found to cause building of hazardousperoxides which may present a safety issue when used on an industrialscale to manufacture fluoropolymers. The polymers disclosed in this U.S.patent are used as a base material of a salt electrolyticcation-exchanged film.

Alkanes have also been disclosed as chain transfer agents in an aqueousemulsion polymerization. For example, U.S. Pat. No. 3,635,926 disclosesthe use methane or ethane to make copolymers of tetrafluoroethylene andperfluorovinyl ethers.

WO 00/32655 discloses the use of hydrofluoroethers (HFEs) for thefluoromonomer emulsion-polymerization. These HFEs are taught to besuperior to common chain transfer agents such as chloroform in beingsafer and environmentally benign. These liquid components are alsotaught to be superior to gaseous chain transfer agents such as ethanebecause they do not enter the fluoromonomer gas recycle streams.However, the chain transfer activity of HFEs is fairly low, making themgenerally only practical in producing perfluorinated polymers where onlya low chain transfer activity is desired and needed. When using the HFEsin producing partially fluorinated fluoropolymers, one will generallyneed a large amount of chain transfer, which is undesirable.

In JP 1-129005 there is disclosed the use of dialkyl ether chaintransfer agents that have not more than 6 carbon atoms in a suspensionpolymerization of vinylidene fluoride to produce homo- or copolymers ofvinylidene fluoride. Specifically disclosed ethers include dimethylether and diethyl ether with the latter being preferred. Thepolymerization temperature is taught to be between 10 and 25° C. It isdisclosed that the use of these chain transfer agents allow for controlof molecular weight of the vinylidene fluoride polymer withoutsubstantially affecting the polymerization rate and the heat resistanceof the polymer produced.

A commonly employed chain transfer agent in the production offluorothermoplasts and fluoroelastomers is diethylmalonate. The use ofdiethylmalonate is for example recommended in EP 43 948 to producecopolymers of TFE and E, such as for example copolymers of TFE, E, HFPand PVE. However, it has been found that fluoropolymers produced in thepresence of this chain transfer agent are susceptible to discoloration,may produce an unpleasant smell and have a high amount of extractablecompounds. Also, the fluoropolymers so produced have been found to havea large amount of low molecular weight fraction which causes processingdifficulties of the fluoropolymer. Furthermore, the yield of thesepolymers when produced through aqueous emulsion polymerization in thepresence of diethylmalonate would desirably be improved.

Further known chain transfer agents used in aqueous emulsionpolymerization include silanes as disclosed in U.S. Pat. Nos. 5,256,745and 5,208,305. However, also in this instance, it was found that thefluoropolymers produced have undesirable properties such asdiscoloration and low purity, in particular high amounts of extractablecompounds. Additionally, the process disclosed in these patents toproduce a bimodal molecular weight distribution of the fluoropolymer iscumbersome, e.g., the polymerization time is long and the polymerizationinitiation is often retarded.

It would thus be desirable to improve the aqueous emulsionpolymerization process so as to produce fluoropolymers with improvedproperties. It is in particular a desire to produce fluoropolymers thathave a high purity, less extractable compounds, less smell, improvedprocessing and less discoloration. It is further desirable to producepartially fluorinated fluoroelastomers and fluorothermoplasts that haveimproved mechanical and physical properties. Desirably, the chaintransfer agents have a high chain transfer activity such that they canbe used in low amounts.

SUMMARY OF THE INVENTION

The present invention provides a method of making a fluoropolymercomprising repeating units derived from one or more gaseous fluorinatedmonomers. The method comprises an aqueous emulsion polymerization of thegaseous fluorinated monomer(s) optionally in combination with one ormore liquid fluorinated monomers in the presence of an ether selectedfrom the group consisting of dimethyl ether (DME), methyl tertiary butylether (MTBE) and mixtures thereof.

It has been found that by using the specific ethers as a chain transferagent, improved fluoropolymers, in particular fluorothermoplasts andfluoroelastomers can be produced. The fluoropolymers produced with theprocess of the present invention generally have a high purity and lowamounts of extractable compounds including residual chain transfer agentand low molecular weight fractions. The ether chain transfer agents donot act as swelling agent for the polymer, in contrast to e.g.diethylmalonate, and are therefore more easy to remove afterpolymerization. The fluoropolymers produced generally are more easy toprocess, produce less smell and are better performing. For example, ithas been found that the process of this invention allows for makingfluorothermoplastic copolymers of E and TFE that have equal or betterphysical and mechanical properties such as e.g. heat resistance asfluorothermoplastic copolymers of E and TFE produced by polymerizationsin organic solvent. Thus, the fluorothermoplastic copolymers of E andTFE produced with the present invention have excellent properties foruse in wire and cable insulation. Further, it has been found that duringextrusion of fluoropolymers made according to the invention, lesspressure fluctuations occur and the amount of die drool formed isgenerally reduced as well.

Additionally, the fluoropolymers can be produced in a convenient andfast way and at good yield (e.g. high solids contents), making theprocess also attractive from an economic perspective. Further because ofthe higher purity and lower amount of extractable compounds, thepolymers produced with the process of this invention will generally alsobe more environmental friendly. Also, DME and MTBE are ethers that donot generally form peroxide (see Bretherick, L. in: Handbook of reactivechemical hazards; p. 549, Butterworth-Heinemann Ltd 1990, ISBN0,7506,0706,8) and can therefore more safely be handled than otherethers, in particular other dialkyl ethers, in the polymerizationprocess of this invention.

The ethers are particularly suitable for producing partially fluorinatedpolymers and because of their high chain transfer activity can be usedin low amounts. Additionally, the ethers have high water solubility andas a result thereof, will despite their gaseous nature not readily enterthe gas stream of gaseous fluorinated monomers that may be used in anemulsion polymerisation process.

Additionally, it has been found that the ethers can be used to producefluoropolymers, in particular fluoroelastomers that have a multi-modal,e.g. a bimodal, molecular weight distribution in a single steppolymerization. By ‘single step’ polymerization is meant that thepolymerization can be carried out without having to interrupt thepolymerization reaction as has been practiced in the prior art where, inorder to produce bimodal fluoropolymers, a first polymer is produced andseparately a second one which are then blended together. Further, suchmulti-modal polymers can be produced with a low level of extractablecompounds.

Thus, in a further aspect, the invention also relates to a fluoropolymerhaving a multi-modal molecular weight distribution, in particular abimodal molecular weight distribution, and comprising less than 12% byweight, preferably less than 10% by weight, most preferably less than 8%by weight based on the weight of fluoropolymer of extractable compoundsas measured by leaving the fluoropolymer in methyl ethyl ketone for 70hours at 40° C.

The process of the present invention also allows for a convenientmanufacturing of so-called “core-shell” polymers by feeding differentmonomers at different stages during the polymerization or by changingthe ratio of the monomers during the polymerization process. Using theether chain transfer agents, an amorphous (elastomeric) core of adesired molecular weight may be polymerized during a first stage of thepolymerization and during a second stage later in the polymerizationprocess a semi-crystalline shell with a desired molecular weight may bepolymerized. Of course the core can also be semi-crystalline and theshell can be made amorphous (as disclosed in U.S. Pat. No. 6,310,141) orboth core and shell may be semi-crystalline (as disclosed in WO00/69969) or amorphous. The process of the present invention allows fora convenient manufacturing of such core-shell polymers in a one singlestep polymerization.

Finally, such core-shell polymers can be produced with a low amount ofextractable compounds and the invention thus also relates to suchcore-shell polymers.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, DME or MTBE or a mixture thereof isused as a chain transfer in the aqueous emulsion polymerization.

The amount of chain transfer agent used in the polymerization isgenerally selected to achieve the desired molecular weight of thefluoropolymer. Typically, the amount of chain transfer agent used willbe between 0.1 and 20 g per kg of polymer produced, more preferablybetween 0.3 and 9 g per kg of polymer produced.

Generally, the aqueous emulsion polymerization process is carried out inthe presence of a fluorinated surfactant, typically a non-telogenicfluorinated surfactant. Suitable fluorinated surfactants include anyfluorinated surfactant commonly employed in aqueous emulsionpolymerization. Particularly preferred fluorinated surfactants are thosethat correspond to the general formula:

Y—R_(f)—Z—M  (III)

wherein Y represents hydrogen, Cl or F; R_(f) represents a linear orbranched perfluorinated alkylene having 4 to 10 carbon atoms; Zrepresents COO⁻ or SO₃ ⁻ and M represents an alkali metal ion or anammonium ion. Most preferred fluorinated surfactants for use in thisinvention are the ammonium salts of perfluorooctanoic acid andperfluorooctane sulphonic acid. Mixtures of fluorinated surfactants canbe used.

The aqueous emulsion polymerization process is generally conducted inthe commonly known manner. The reactor vessel is typically apressurizable vessel capable of withstanding the internal pressuresduring the polymerization reaction. Typically, the reaction vessel willinclude a mechanical agitator, which will produce thorough mixing of thereactor contents and heat exchange system.

Any quantity of the fluoromonomer(s) may be charged to the reactorvessel. The monomers may be charged batchwise or in a continuous orsemicontinuous manner. By semi-continuous is meant that a plurality ofbatches of the monomer are charged to the vessel during the course ofthe polymerization. The independent rate at which the monomers are addedto the vessel will depend on the consumption rate of the particularmonomer with time. Preferably, the rate of addition of monomer willequal the rate of consumption of monomer, i.e. conversion of monomerinto polymer.

The reaction vessel is charged with water, the amounts of which are notcritical. To the aqueous phase there is generally also added thefluorinated surfactant which is typically used in amount of 0.01% byweight to 1% by weight. The chain transfer agent is typically charged tothe reaction vessel prior to the initiation of the polymerization.Further additions of chain transfer agent in a continuous orsemi-continuous way during the polymerization may also be carried out.For example, a fluoropolymer having a bimodal molecular weightdistribution is conveniently prepared by first polymerizing fluorinatedmonomer in the presence of an initial amount of chain transfer agent andthen adding at a later point in the polymerization further chaintransfer agent together with additional monomer.

The polymerization is usually initiated after an initial charge ofmonomer by adding an initiator or initiator system to the aqueous phase.For example peroxides can be used as free radical initiators. Specificexamples of peroxide initiators include, hydrogen peroxide, sodium orbarium peroxide, diacylperoxides such as diacetylperoxide,dipropionylperoxide, dibutyrylperoxide, dibenzoylperoxide,benzoylacetylperoxide, diglutaric acid peroxide and dilaurylperoxide,and further water soluble per-acids and water soluble salts thereof suchas e.g. ammonium, sodium or potassium salts. Examples of per-acidsinclude peracetic acid. Esters of the peracid can be used as well andexamples thereof include tert.-butylperoxyacetate andtert.-butylperoxypivalate. A further class of initiators that can beused are water soluble azo-compounds. Suitable redox systems for use asinitiators include for example a combination of peroxodisulphate andhydrogen sulphite or disulphite, a combination of thiosulphate andperoxodisulphate or a combination of peroxodisulphate and hydrazine.Further initiators that can be used are ammonium- alkali- or earthalkali salts of persulfates, permanganic or manganic acid or manganicacids. The amount of initiator employed is typically between 0.03 and 2%by weight, preferably between 0.05 and 1% by weight based on the totalweight of the polymerization mixture. The full amount of initiator maybe added at the start of the polymerization or the initiator can beadded to the polymerization in a continuous way during thepolymerization until a conversion of 70 to 80%. One can also add part ofthe initiator at the start and the remainder in one or separateadditional portions during the polymerization. Accelerators such as forexample water-soluble salts of iron, copper and silver may preferablyalso be added.

During the initiation of the polymerization reaction, the sealed reactorvessel and its contents are pre-heated to the reaction temperature.Preferred polymerization temperatures are from 30° C. to 80° C. and thepressure is typically between 4 and 30 bar, in particular 8 to 20 bar.

The aqueous emulsion polymerization system may further compriseauxiliaries, such as buffers and complex-formers.

The amount of polymer solids that can be obtained at the end of thepolymerization is typically between 10% and 45% by weight, preferablybetween 20% and 40% by weight and the average particle size of theresulting fluoropolymer is typically between 50 nm and 500 nm.

According to a further embodiment of the present invention, the aqueousemulsion polymerization may also be carried out without the addition ofa fluorinated surfactant. Aqueous emulsion polymerization that iscarried out without the addition of a fluorinated surfactant can bepracticed as disclosed in U.S. Pat. No. 5,453,477 and WO 97/17381.According to the emulsifier free aqueous emulsion polymerizationdisclosed in WO 97/17381 a radical initiator system of a reducing agentand oxidizing agent is used to initiate the polymerization and theinitiator system is added in one or more further charges during thepolymerization. The ionic end groups formed as a result of the initiatorsystem used in WO 97/17381 are taught to stabilise the fluoropolymerparticles in the emulsifier free aqueous emulsion process. Suitableoxidizing agents that can be used include persulfates such as potassiumsulfate and ammonium sulfate, peroxides such as hydrogen peroxide,potassium peroxide, ammonium peroxide, tertiary butyl hydroperoxide,cumene peroxide and t-amyl hydroperoxide, manganese triacetate,potassium permanganate, ascorbic acid and mixtures thereof. Suitablereducing agents include sodium sulfites such as sodium bisulfite, sodiumsulfite, sodium pyrosulfite, sodium-m-bitsulfite, ammonium sulfitemonohydrate and sodium thiosulphate, hydroxylamine, hydrazine, ferrousiron, organic acids such as oxalic acid and citric acid and mixturesthereof.

The amount of oxidizing agent added in the initial charge is typicallybetween 10 and 10000 ppm. The amount of reducing agent in the initialcharge is typically also between 10 and 10000 ppm. At least one furthercharge of oxidizing agent and reducing agent is added to thepolymerization system in the course of the polymerization. The furtheraddition(s) may be done batchwise or the further addition may becontinuous.

According to a preferred embodiment, an emulsifier free (i.e. withoutadded emulsifier) aqueous polymerization involves an initial charge ofan oxidizing agent and a reducing agent and one or more further chargesof either the reducing agent or oxidizing agent, but not both, in thecourse of the polymerization. This embodiment of the invention has theadvantage that the aqueous polymerization process can be conducted in aneasy and convenient way while still yielding stable polymer dispersionsat a high rate and in good yield.

The aqueous emulsion polymerization process of the present inventioncomprises the polymerization of at least one gaseous fluorinatedmonomer. According to a particular embodiment of the present invention,the aqueous emulsion polymerization involves a copolymerization of agaseous fluorinated monomer such as tetrafluoroethylene,chlorotrifluoroethylene and vinylidene fluoride and a comonomer selectedfrom the group consisting of vinylidene fluoride, perfluoroalkyl vinylmonomers, ethylene, propylene, fluorinated allyl ethers, in particularperfluorinated allyl ethers and fluorinated vinyl ethers, in particularperfluorovinyl ethers. Additional fluorinated and non-fluorinatedmonomers can be included as well. It will be understood by one skilledin the art that when the polymerization involves vinylidene fluoride,the gaseous fluorinated monomer would generally be eithertetrafluoroethylene or chlorotrifluoroethylene or a comonomer other thanvinylidene fluoride would have to be selected to obtain a copolymer.Examples of perfluorovinyl ethers that can be used in the process of theinvention include those that correspond to the formula:

CF₂═CF—O—R_(f)

wherein R_(f) represents a perfluorinated aliphatic group that maycontain one or more oxygen atoms.

Particularly preferred perfluorinated vinyl ethers correspond to theformula:

CF₂═CFO(R^(a) _(f)O)_(n)(R^(b) _(f)O)_(m)R^(c) _(f)

wherein R^(a) _(f) and R^(b) _(f) are different linear or branchedperfluoroalkylene groups of 1-6 carbon atoms, in particular 2 to 6carbon atoms, m and n are independently 0-10 and R^(c) _(f) is aperfluoroalkyl group of 1-6 carbon atoms. Specific examples ofperfluorinated vinyl ethers include perfluoro methyl vinyl ether (PMVE),perfluoro n-propyl vinyl ether (PPVE-1), perfluoro-2-propoxypropylvinylether (PPVE-2), perfluoro-3-methoxy-n-propylvinyl ether,perfluoro-2-methoxy-ethylvinyl ether and

CF₃—(CF₂)₂—O—CF(CF₃)—CF₂—O—CF(CF₃)—CF₂—O—CF═CF₂.

Suitable perfluoroalkyl vinyl monomers correspond to the generalformula:

CF₂═CF—R^(d) _(f) or CH₂═CH—R^(d) _(f)

wherein R^(d) _(f) represents a perfluoroalkyl group of 1 to 10,preferably 1 to 5 carbon atoms. A typical example of a perfluoroalkylvinyl monomer is hexafluoropropylene.

The process of the present invention is preferably used for producingfluoropolymers that have a partially fluorinated backbone, i.e. part ofthe hydrogen atoms on the backbone are replaced with fluorine.Accordingly, the aqueous polymerization process of the present inventionwill generally involve at least one monomer that has an ethylenicallyunsaturated group that is partially fluorinated (e.g. vinylidenefluoride) or not fluorinated (e.g. ethylene or propylene). It has beenfound that the ethers are highly effective chain transfer agent for usewith monomers that have a non-fluorinated or partially fluorinatedethylenically unsaturated group. On the other hand, they can be used toproduce perfluoropolymers, i.e. polymers that have a fully fluorinatedbackbone.

Examples of fluoropolymers that are preferably produced with the processof the invention include a copolymer of vinylidene fluoride andhexafluoropropylene, a copolymer of tetrafluoroethylene and vinylidenefluoride, a copolymer of chlorotrifluoroethylene and vinylidenefluoride, a copolymer of tetrafluoroethylene and ethylene, a copolymerof tetrafluoroethylene and propylene, a copolymer of vinylidene fluorideand perfluorovinyl ether (e.g. PMVE, PPVE-1, PPVE-2 or a combination ofPPVE-1 and PPVE-2), a terpolymer of tetrafluoroethylene, ethylene orpropylene and perfluorovinyl ether (e.g. PMVE, PPVE-1, PPVE-2 or acombination of PPVE-1 and PPVE-2), a copolymer of tetrafluoroethylene,ethylene or propylene and hexafluoropropylene, a copolymer oftetrafluoroethylene, vinylidene fluoride and hexafluoropropylene, acopolymer of vinylidene fluoride, tetrafluoroethylene and perfluorovinylether (e.g. PMVE, PPVE-1, PPVE-2 or a combination of PPVE-1 and PPVE-2),and a co-polymer of a copolymer of tetrafluoroethylene, ethylene orpropylene, hexafluoropropylene and perfluorovinyl ether (e.g. PMVE,PPVE-1, PPVE-2 or a combination of PPVE-1 and PPVE-2).

The fluoropolymers that can be produced with the process of theinvention are generally amorphous fluoropolymers or semi-crystallinefluoropolymers. A fluoroelastomer is generally a fluoropolymer havingelastomeric properties upon curing and will generally not display amelting peak or will have a very minor melting peak, i.e. thefluoroelastomer will generally have little or no crystallinity.Fluorothermoplasts are polymers that generally have a pronounced meltingpeak and that generally have crystallinity. The fluorothermoplastsaccording to this invention will generally be melt processible, i.e.they will typically have a melt flow index of at least 0.1 g/10 min. asmeasured with a load of 5 kg and at a temperature of 265° C. as set outin the examples below. Whether the particular fluoropolymer produced isa fluorothermoplast or fluoroelastomer, depends on the nature andamounts of the monomers from which the fluoropolymer is derived as iswell known to those skilled in the art.

The fluoropolymers produced with the process of the invention can have amulti-modal including a bimodal molecular weight distribution which canprovide advantageous processing properties. In particular, suchmulti-modal fluoropolymers may be produced by charging no or a smallinitial amount of ether at the beginning of the polymerization, e.g.prior to the addition of initiator, and one or more further charges ofthe ether during the polymerization. Accordingly, fluoropolymers with amulti-modal molecular weight distribution can conveniently be producedin a single step polymerization.

Fluorothermoplasts

Fluorothermoplasts that can be produced with the process of the presentinvention generally will have a melting point between 50° C. and 300°C., preferably between 60° C. and 280° C. Particularly desirablefluorothermoplasts that can be produced with the process of thisinvention include for example copolymers of E and TFE, copolymers of TFEand VDF, copolymers of VDF and HFP, copolymers of CTFE and VDF,copolymers of TFE, E and HFP and copolymers of TFE, HFP and VDF.

Fluorothermoplasts that may be produced in connection with the presentinvention generally have the advantage of being less susceptible todiscoloration, having a decreased amount of extractable compounds andhaving a high purity and generally are more homogeneous, e.g. thepolymer doesn't show a drift of the melt flow index duringpolymerizaton. Accordingly, the fluorothermoplasts are generally moreeasy to process and generally have high temperature resistance, highchemical resistance, same or improved electrical properties good moldrelease and reduced amount of smell. Further, the fluorothermoplastswhen extruded typically produce less die drool.

The fluorothermoplastic polymers that can be obtained with the processof the present invention can be used in any of the applications in whichfluorothermoplasts are typically used. For example, thefluorothermoplasts can be used to insulate wires and cables. Inparticular a copolymer of E and TFE produced with the process of thisinvention has been found to have highly desirable properties to insulatewires. To produce a cable or wire insulated with a fluorothermoplastaccording to the invention, in particular a copolymer of E and TFE, thefluorothermoplast can be melt extruded around a central conductor, e.g.copper wire. A conductive metallic layer may be formed around theextruded fluorothermoplast layer to produce for example a heating cable.

The fluorothermoplastic polymers produced may further be used to makehoses, in particular fuel hoses and pipes and can be used in particularin heat exchange applications. The fluorothermoplasts may also beextruded into a film or into so-called mono filaments which may thensubsequently be woven into a woven fabric. Still further, thefluorothermoplasts can be used in coating applications for example tocoat outdoor fabric or to make injection molded articles.

Fluoroelastomers

In addition to fluorothermoplasts, the process of the present inventionalso allows for making fluoroelastomers with desirable and improvedproperties. In particular, the fluoroelastomers produced will generallyhave a higher purity, a lesser amount of extractable compounds, willgenerally be less susceptible to discoloration, more easy to process andwill typically produce less smell. Additionally, the mechanical andphysical properties of the fluoroelastomers may be improved by theprocess of the invention. For example, a curable fluoroelastomerproduced according to the invention may have an improved compression setand may have same or improved permeation properties.

Fluoroelastomers that can be produced in connection with the presentinvention include elastomers that are not fully fluorinated. Thefluoroelastomer may include a cure site component, in particular one ormore cure sites derived from a cures site monomer (CSM) to provide acurable fluoroelastomer. Specific examples of elastomeric copolymersinclude copolymers comprising a combination of monomers as follows:VDF-HFP, VDF-TFE-HFP, VDF-TFE-HFP-CSM, VDF-TFE-PMVE-CSM, TFE-P,E-TFE-PMVE-CSM and TFE-VDF-P-CSM.

To obtain a curable fluoroelastomer, a further cure site component maybe included in the polymerization reaction to obtain a curablefluoroelastomer. Generally, the cure site component will be used insmall amounts, typically in amounts so as to obtain a fluoroelastomerthat has between 0.1 and 5 mol % of cure sites, preferably 0.2 to 3 mol% and most preferred 0.5-2 mol %.

The cure site component may comprise a nitrile group-containing curesite monomer. The cure site component can be partially or fullyfluorinated. Preferred useful nitrile group-containing cure sitemonomers include nitrile-containing fluorinated olefins andnitrile-containing fluorinated vinyl ethers, such as depicted below:

CF₂═CF—(CF₂)_(n)—O—R_(f)—CN

CF₂═CFO(CF₂)_(l)CN

CF₂═CFO[CF₂CF(CF₃)O]_(g)(CF₂O)_(v)CF(CF₃)CN

CF₂═CF[OCF₂CF(CF₃)]_(k)O(CF₂)_(u)CN

where, in reference to the above formulas: n=1 to 5l; 1=2-12; g=0-4;k=1-2; v=0-6; and u=1-4, R_(f) is a linear or branched perfluoroalkyleneor a bivalent perfluoroether group. Representative examples of such amonomer include perfluoro(8-cyano-5-methyl-3,6-dioxa-1-octene),CF₂═CFO(CF₂)₅CN, and CF₂═CFO(CF₂)₃OCF(CF₃)CN.

Alternatively, the cure site component may comprise a fluorinatedmonomer having a halogen capable of participation in a peroxide curereaction. Typically the halogen is bromine or iodine. Suitable cure-sitecomponents include terminally unsaturated monoolefins of 2 to 4 carbonatoms such as bromodifluoroethylene, bromotrifluoroethylene,iodotrifluoroethylene, and 4-bromo-3,3,4,4-tetrafluorobutene-1. Examplesof other suitable cure site components include CF₂═CFOCF₂CF₂Br,CF₂═CFOCF₂CF₂CF₂Br, and CF₂═CFOCF₂CF₂CF₂OCF₂CF₂Br. Preferably, all oressentially all of these components are ethylenically unsaturatedmonomers.

A curable fluoroelastomer composition will generally include the curablefluoroelastomer and one or more curatives such as the peroxide and/orone or more catalysts depending on the type of cure sites contained inthe curable fluoroelastomer. Suitable peroxide curatives are those whichgenerate free radicals at curing temperatures. A dialkyl peroxide or abis(dialkyl peroxide) which decomposes at a temperature above 50° C. isespecially preferred. In many cases it is preferred to use adi-tertiarybutyl peroxide having a tertiary carbon atom attached toperoxy oxygen. Among the most useful peroxides of this type are2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexyne-3 and2,5-dimethyl-2,5-di(tertiarybutylperoxy)hexane. Other peroxides can beselected from such compounds as dicumyl peroxide, dibenzoyl peroxide,tertiarybutyl perbenzoate, α,α′-bis(t-butylperoxy-diisopropylbenzene),and di[1,3-dimethyl-3-(t-butylperoxy)-butyl]carbonate. Generally, about1-3 parts of peroxide per 100 parts of perfluoroelastomer is used.

Another material which is usually blended with the composition as a partof the curative system is a coagent composed of a polyunsaturatedcompound which is capable of cooperating with the peroxide to provide auseful cure. These coagents can be added in an amount equal to 0.1 and10 parts per hundred parts perfluoroelastomer, preferably between 2-5parts per hundred parts fluoroelastomer. Examples of useful coagentsinclude triallyl cyanurate; triallyl isocyanurate; tri(methylallylisocyanurate; tris(diallylamine)-s-triazine; triallyl phosphite;N,N-diallyl acrylamide; hexaallyl phosphoramide; N,N,N′,N′-tetraalkyltetraphthalamide; N,N,N′,N′-tetraallyl malonamide; trivinylisocyanurate; 2,4,6-trivinyl methyltrisiloxane; andtri(5-norbornene-2-methylene)cyanurate. Particularly useful is triallylisocyanurate. Other useful coagents include the bis-olefins disclosed inEPA 0 661 304 A1, EPA 0 784 064 A1 and EPA 0 769 521 A1.

When the fluoroelastomer includes a nitrile containing cure sitecomponent, a catalyst comprising one or more ammonia-generatingcompounds may be used to cause curing. “Ammonia-generating compounds”include compounds that are solid or liquid at ambient conditions butthat generate ammonia under conditions of cure. Such compounds include,for example, aminophenols as disclosed in U.S. Pat. No. 5,677,389,ammonia salts (U.S. Pat. No. 5,565,512), amidoxines (U.S. Pat. No.5,668,221), imidates, hexamethylene tetramine (urotropin), dicyandiamid, and metal-containing compounds of the formula:

A^(w+)(NH₃)_(v)Y^(w−)

where A^(w+) is a metal cation such as Cu²⁺, Co²⁺, Co³⁺, Cu⁺, and Ni²⁺;w is equal to the valance of the metal cation; Y^(w−) is a counterion,typically a halide, sulfate, nitrate, acetate or the like; and v is aninteger from 1 to about 7. Still further ammonia generating compoundsare disclosed in PCT 00/09603.

Fluoroelastomers, in particular VDF containing fluoroelastomers, mayfurther be cured using a polyhydroxy curing system. In such instance, itwill not be required that the fluoroelastomer includes cure sitecomponents. The polyhydroxy curing system generally comprises one ormore polyhydroxy compounds and one or more organo-onium accelerators.The organo-onium compounds useful in the present invention typicallycontain at least one heteroatom, i.e., a non-carbon atom such as N, P,S, O, bonded to organic or inorganic moieties. One useful class ofquaternary organo-onium compounds broadly comprises relatively positiveand relatively negative ions wherein a phosphorus, arsenic, antimony ornitrogen generally comprises the central atom of the positive ion, andthe negative ion may be an organic or inorganic anion (e.g., halide,sulfate, acetate, phosphate, phosphonate, hydroxide, alkoxide,phenoxide, bisphenoxide, etc.).

Many of the organo-onium compounds useful in this invention aredescribed and known in the art. See, for example, U.S. Pat. No.4,233,421 (Worm), U.S. Pat. No 4,912,171 (Grootaert et al.), U.S. Pat.No 5,086,123 (Guenthner et al.), and U.S. Pat. No 5,262,490 (Kolb etal.), U.S. Pat. No. 5,929,169, all of whose descriptions are hereinincorporated by reference. Another class of useful organo-oniumcompounds include those having one or more pendent fluorinated alkylgroups. Generally, the most useful fluorinated onium compounds aredisclosed by Coggio et al. in U.S. Pat. No. 5,591,804.

The polyhydroxy compound may be used in its free or non-salt form or asthe anionic portion of a chosen organo-onium accelerator. Thecrosslinking agent may be any of those polyhydroxy compounds known inthe art to function as a crosslinking agent or co-curative forfluoroelastomers, such as those polyhydroxy compounds disclosed in U.S.Pat. No. 3,876,654 (Pattison), and U.S. Pat. No 4,233,421 (Worm). One ofthe most useful polyhydroxy compounds includes aromatic polyphenols suchas 4,4′-hexafluoroisopropylidenyl bisphenol, known more commonly asbisphenol AF. The compounds 4,4′-dihydroxydiphenyl sulfone (also knownas Bisphenol S) and 4,4′-isopropylidenyl bisphenol (also known asbisphenol A) are also widely used in practice.

Prior to curing, an acid acceptor is mixed into a fluoroelastomercomposition that comprises a polyhydroxy cure system. Acid acceptors canbe inorganic or blends of inorganic and organic. Examples of inorganicacceptors include magnesium oxide, lead oxide, calcium oxide, calciumhydroxide, dibasic lead phosphite, zinc oxide, barium carbonate,strontium hydroxide, calcium carbonate, etc. Organic acceptors includeepoxies, sodium stearate, and magnesium oxalate. The preferred acidacceptors are magnesium oxide and calcium hydroxide. The acid acceptorscan be used singly or in combination, and preferably are used in amountsranging from about 2 to 25 parts per 100 parts by weight of thefluoroelastomer.

A curable fluoroelastomer composition may comprise further additives,such as carbon black, stabilizers, plasticizers, lubricants, fillers,and processing aids typically utilized in fluoroelastomer compoundingcan be incorporated into the compositions, provided they have adequatestability for the intended service conditions.

Carbon black fillers are typically also employed in elastomers as ameans to balance modulus, tensile strength, elongation, hardness,abrasion resistance, conductivity, and processability of thecompositions. Suitable examples include MT blacks (medium thermal black)designated N-991, N-990, N-908, and N-907, and large particle sizefurnace blacks. When used, 1-70 phr of large size particle black isgenerally sufficient.

Fluoropolymer fillers may also be present in the curable compositions.Generally, from 1 to 50 parts per hundred fluoroelastomer of afluoropolymer filler is used. The fluoropolymer filler can be finelydivided and easily dispersed as a solid at the highest temperatureutilized in fabrication and curing of the fluoroelastomer composition.By solid, it is meant that the filler material, if partiallycrystalline, will have a crystalline melting temperature above theprocessing temperature(s) of the fluoroelastomer(s). The most efficientway to incorporate fluoropolymer filler is by blending latices; thisprocedure including various kinds of fluoro polymer filler is describedin U.S. application Ser. No. 09/495600, filed Feb. 1, 2000.

The curable compositions can be prepared by mixing the fluoroelastomer,the curatives and/or catalysts, the selected additive or additives, andthe other adjuvants, if any, in conventional rubber processingequipment. The desired amounts of compounding ingredients and otherconventional adjuvants or ingredients can be added to the unvulcanizedfluorocarbon gum stock and intimately admixed or compounded therewith byemploying any of the usual rubber mixing devices such as internalmixers, (e.g., Banbury mixers), roll mills, or any other convenientmixing device. For best results, the temperature of the mixture duringthe mixing process typically should not rise above about 120° C. Duringmixing, it is preferable to distribute the components and adjuvantsuniformly throughout the gum for effective cure. The mixture is thenprocessed and shaped, for example, by extrusion (for example, in theshape of a hose or hose lining) or molding (for example, in the form ofan O-ring seal). The shaped article can then be heated to cure the gumcomposition and form a cured elastomer article.

Pressing of the compounded mixture (i.e., press cure) usually isconducted at a temperature between about 95° C. and about 230° C.,preferably between about 150° C. and about 205° C., for a period of from1 minute to 15 hours, typically from 5 minutes to 30 minutes. A pressureof between about 700 kPa and about 20,600 kPa is usually imposed on thecompounded mixture in the mold. The molds first may be coated with arelease agent and prebaked. The molded vulcanizate is then usuallypost-cured (e.g., oven-cured) at a temperature usually between about150° C. and about 300° C., typically at about 232° C., for a period offrom about 2 hours to 50 hours or more depending on the cross-sectionalthickness of the article. For thick sections, the temperature during thepost cure is usually raised gradually from the lower limit of the rangeto the desired maximum temperature. The maximum temperature used ispreferably about 300° C., and is held at this value for about 4 hours ormore.

The curable fluoroelastomer compositions are useful in production ofarticles such as gaskets, tubing, and seals. Such articles are producedby molding a compounded formulation of the curable composition withvarious additives under pressure, curing the part, and then subjectingit to a post cure cycle. The curable compositions formulated withoutinorganic acid acceptors are particularly well suited for applicationssuch as seals and gaskets for manufacturing semiconductor devices, andin seals for high temperature automotive uses.

The invention will now be further illustrated with reference to thefollowing examples without the intention to limit the invention thereto.All parts and percentages are by weight unless indicated otherwise.

EXAMPLES

Test Methods Used:

The melt flow index (MFI) was carried out according to DIN 53735, ISO12086 or ASTM D-1238 at a support weight of 5.0 kg and a temperature of265° C. or 297° C. alternatively. The MFIs cited here were obtained witha standardized extrusion die of 2.1 mm diameter and a length of 8.0 mm.

Mooney viscosities were determined in accordance with ASTM D1646. Unlessotherwise noted, the Mooney viscosity was determined from compositionscontaining fluoroelastomer incorporating curatives or the final compoundusing a 1 minute pre-heat and a 10 minute test at 121° C. (ML 1+10@121°C.).

A Monsanto Processability Tester (MPT) was used to evaluate theprocessability of the fluoropolymer. Hereby, the pressures weredetermined that were required to extrude each compound at shear rates of180, 361, 726 and 1446 l/s. The instrument was equipped with a 1.50 mmdiameter die of L/D=10, all compounds were tested at 105° C. unlessotherwise noted.

76×152×2 mm press cured sheets were prepared for physical propertytesting by pressing at 5 to 7 MPa at 163° C. for 50 minutes. From thesepress cured sheets, the Tensile Strength at Break and the Elongation atBreak were measured according to ASTM D 412. Hardness was determinedaccording to ASTM D2240 Method A, Shore A durometer was used. Thecompression set was determined according to ASTM 395-89, Method B.

Melting peaks of the fluororesins were determined according to ASTM 4591by means of Perkin-Elmer DSC 7.0 under nitrogen flow and a heating rateof 10° C./min. The indicated melting points relate to the melting peakmaximum.

In accordance with DIN 5033, the L/a/b color values were measured frompress cured plates against a white ceramic plate background (standardHDF 067-01-0785) using a Dr. Lange Micro Color 2 instrument (type LGC20-2, equipped with a norm D65 light source). As the color b-valuerepresents the blue to yellow color axis, the b-value is the bestmeasure to quantify discoloration—slightly negative b-values appear asblue hue and positive b-value appear as yellow.

Solution viscosity of diluted polymer solutions was determined on a 0.2%polymer solution in methylethylketone (MEK) at 35° C. in accordance toDIN 53726. A Connon-Fenske-Routine-Viskosimeter (Fa. Schott,Mainz/Germany) fulfilling ISO/DIS 3105 and ASTM D 2515 was used for themeasurements.

Solution viscosities of concentrated polymer solutions (40% polymersolution in N,N′-dimethylacetamide) were measured according to DIN 53019using a Physica Rheolab MCl rotational viscosimeter (Couette-geometryaccording to Z2-DIN).

Molecular weight distributions were determined by means of SizeExclusion Chromatography (SEC) recorded at 35° C. in tetrahydrofuran-UVgrade. The SEC equipment consisted of a Waters 510 isocratic pump, aPerkin Elmer ISS-100 autosampler, a Waters column oven, three gel mixedbed type B columns (10 μm) from Polymer Laboratories (300 mm×7.5 mm),and a Waters 410 RI detector. The instrument was calibrated using 10narrow distributed polystyrene standard samples (PSS, Mainz/Germany)ranging from 1280 g/mol to 7300000 g/mol. The SEC-elugrams calibrated topolystyrene were converted to the molecular weight distribution with theuniversal calibration procedure using the Mark-Houwink coefficientsα=0.751 and K=0.045396 ml/g.

The latex particle size determination was conducted by means of dynamiclight scattering with a Malvern Zetazizer 1000 HSA in accordance toISO/DIS 13321. Prior to the measurements, the polymer latexes as yieldedfrom the polymerizations were diluted with 0.001 mol/L KCl-solution, themeasurement temperature was 20° C. in all cases.

For the evaluation of the vapor transmission (permeation rate) inaccordance to ASTM D814, a mixture of 42.5% toluene, 42.5% isooctane and15% methanol by volume was used as test fluid. Sheets of 0.75-0.90 mmthickness of each polymer composition were press-cured. 3 inch diametersamples were die cut from each sheet. Vapor transmission cups, each witha 2.5 inch opening (4.909 in² exposed sample surface) and approximately160 ml capacity, were used and are available from Thwing-AlbertInstrument Co. High fluorine, low durometer fluoroelastomer gasketsinsured a good seal between sample and the test fluid. The cups wereassembled by placing 100 ml of fluid in the cup, a 0.5 mm gasket betweenthe cup and the sample, and a 1.5 mm gasket between the sample and theclamping ring. Because the samples were extensible during testing, a16-mesh circular screen was placed between the upper gasket and theclamping ring. All tests were conducted at 40° C. for 32 days with thecup maintained in the upright position. The first 7 days of testing, nodata were collected in order to allow the sample to reach vaportransmission equilibrium. Then the cups were weighted approximatelyevery other day. The transmission rate was then multiplied by thethickness of the samples in millimeters to normalize each value.

For extractable evaluation, cured elastomer sheets were soaked inmethylethylketone (MEK) for 70 hours at 40° C. After this soak period,the cured gum sheet was removed from MEK. MEK was removed from themother liquor via distillation and the remaining residual was dried for70 hours at 80° C. and weight.

Example 1

A polymerization vessel with a total volume of 186 l equipped with animpeller agitator system was charged with 114.6 l deionized water, 12 goxalic acid, 51 g ammonium oxalate and 320 g perfluorooctanoate ammoniumsalt (APFO). The oxygen free vessel was then heated up to 45° C. and theagitation system was set to 210 rpm. The vessel was charged with 230 gmethyl tertiary butyl ether (MTBE) and 190 g PPVE-2 to a pressure of 0.5bar absolute, with PPVE-1 to 1.26 bar absolute (958 g), with ethylene to3.52 bar absolute (198 g) and with tetrafluoroethylene (TFE) to 15.5 barabsolute (3968 g) reaction pressure. The polymerization was initiated by70 ml of a 3.2% aqueous potassium permanganate solution. As the reactionstarted, the reaction pressure of 15.5 bar absolute was maintained byfeeding TFE, ethylene, PPVE-1 and PPVE-2 into the gas phase with afeeding ratio ethylene (kg)/TFE (kg) of 0.2407, PPVE-1 (kg)/TFE (kg) of0.0956 and PPVE-2 (kg)/TFE (kg) of 0.008. Within the polymerization the3.2% aqueous potassium permanganate solution was continuously chargedinto the vessel with a feeding rate 110 ml/h. A reaction temperature of45° C. was maintained.

After feeding 36.6 kg TFE (236 min polymerization time), the monomerfeed was interrupted and the monomer valves were closed. The addition ofpotassium permanganate solution was maintained at a feed rate of 40ml/h. Within 10 min, the monomer gas phase was reacted down to a vesselpressure of 7.5 bar.

The thus obtained 164.7 kg polymer dispersion consisted of latexparticles having 95 nm in diameter according to dynamic lightscattering.

This polymer dispersion having a solid content of 30.8% was removed atthe bottom of the reactor, passed through a glass column containingDOWEX 650C cation exchange resin (Dow Chemical Co.) and subsequentlytransferred into a 250-l agglomeration vessel. To the polymer dispersionwas added 100 l deionized water, 2.5 l concentrated hydrochloric acidand 35 l perfluoro n-heptane agglomeration aid (PF 5070 by 3M). Theagglomeration vessel was agitated vigorously until the solid had fullyseparated from the aqueous phase. The agglomerate was washed three timeswith deionized water, the agglomeration aid was distilled off and thepolymer was dried in an oven at 130° C. for 12 hours and another 4 hoursat 200° C. to remove all residual moistures. The thus obtained 49 kgpolymer showed a melting point maximum of 254° C. and a heat of fusionof 44 J/g in the DSC trace. The polymer had an MFI(297/5) of 8.5 g/10min. At 23° C., the elongation at break was 457% and the tensilestrength at break was 44.6 MPa. At 200° C., the elongation at break was424% and the tensile strength at break was 2.7 MPa.

This example demonstrates the improved efficiency of the polymerizationprocess using a dialkyl ether chain transfer agent (MTBE) in that thepolymer solid content achieved was well above 30%. This is to becompared with for example the polymerization process disclosed in EP 43948 which uses diethyl malonate (DEM) chain transfer agent wherein thepolymer solid content that can be obtained is generally around 20 to22%.

Example 2 to 4

In the examples 2, 3 & 4, polymers were produced following the procedureof example 1 with the exception that the amount of MTBE chain transferagent was varied (examples 2 & 3) or that dimethylether (Me₂O) was used(example 4). The polymer workup was conducted the same way as inexample 1. The results are summarised in table 1.

TABLE 1 Example 2 Example 3 Example 4 chain transfer agent 250 g MTBE285 g MTBE 310 g Me₂O polymerisation time 4.1 hours 4.3 hours 4.0 hourssolid content 30.8 30.7 30.9 latex particle diameter 98 nm 89 nm 92 nmMFI(297/5) 14.6 28.9 21.8 elongation @ break, 23° C. 462% 455% 470%tensile strength @ break, 43.7 MPa 43.0 MPa 43.1 MPa 23° C. elongation @break, 200° C. 186% 15% 32% tensile strength @ break, 2.6 MPa 2.1 MPa2.3 MPa 200° C. melting point 255° C. 257° C. 254° C.

As can be seen from the examples, the polymer melt viscosity can be wellcontrolled by the amount of dialkyl ether chain transfer agent whileachieving a high polymer yield and short polymerization times as well asmaintaining the physical properties measured on the yielded polymersamples.

Example 5

In this example, the thermal stability of the ETFE copolymer producedfrom example 1 was measured and compared with similar ETFE copolymersfrom the prior art. Comparative sample A was a TFE/E/PPVE-1 copolymerprepared according to the polymerization process disclosed in EP 0 043948 using DEM as a chain transfer agent. Comparative sample B was AflonCOP C-55 AX, an ETFE copolymer commercially available from Asahi GlassCompany and believed to be produced in an organic medium according tothe procedure disclosed in U.S. Pat. No. 4,123,602. Press cured sheetswere prepared (by pressing at 6 MPa at 300° C. for 10 min) from the ETFEcopolymer of example 1 as well as of the two comparative ETFE samples Aand B. Together with melt pellets of all three ETFE samples, thesecompression molded plates were placed into an oven that was heated to175° C. (air atmosphere). After various heat aging times, polymersamples were taken out of the oven and their melt viscosity, themechanical data as well as color values were measured. These data aresummarised in the following tables.

TABLE 2 Heat aging data of ETFE polymer of example 1: tensile strength @storage time MFI break, elongation @ color b- @ 175° C. [h] (297/5) 23°C. [MPa] break, 23° C. [%] value initial values 8.5 44.6 457 −3.6  9 7.639.6 432 −2.1 120 6.7 41.2 459 −0.7 264 6.3 41.0 459 −0.7 508 5.7 41.7468 0.3 1008  5.2 42.7 459 0.9

TABLE 3 Heat aging data of comparative A: tensile strength @ storagetime MFI break, elongation @ Color b- @ 175° C. [h] (297/5) 23° C. [MPa]break, 23° C. [%] value initial values 13.0 47.8 465 −3.4  9 16.8 45.3473 −2.2 120 24 40.4 482 −0.7 264 28 36.6 466 1.5 508 32 32.5 422 14.61008  35 27.2 184 30.6

TABLE 4 Heat aging data of comparative B: tensile strength @ storagetime MFI break, elongation @ color b- @ 175° C. [h] (297/5) 23° C. [MPa]break, 23° C. [%] value initial values  8.9 50.0 441 −3.6  9 10.2 46.5437 −2.6 120 11.4 43.7 436 −1.9 264 12.6 38.2 401 2.0 508 13.7 35.2 41719.0 1008  14.9 33.7 413 32.7

As a comparison of the different sets of the heat aging data shows, thephysical properties of all three samples considered is remarkabledifferent from each other. The comparative samples A and B undergo asubsequent decay of the melt viscosity with increasing heat aging time.The mechanical data (tensile strength and elongation at break) alsofollow this declination of the melt viscosity (which is a measure of themolecular weight). Additionally, both comparative materials undergo adiscoloration and they are deeply discolored after 1000 h heat agingtime. This is quantified with the high color b-values.

The melt viscosity of ETFE polymer of example 1 remains stable and doesnot undergo a discernible thermal degradation for more than 1000 h,whereas the MFI increases with time for the comparative example.Accordingly, this example demonstrates the improved thermal stability ofthe ETFE polymer produced using dialkyl ether chain transfer agentscompared to the prior art materials.

Example 6

A polymerization vessel with a total volume of 186 l equipped with animpeller agitator system was charged with 114.6 l deionized water, 65 goxalic acid, 230 g ammonium oxalate and 410 g perfluorooctanoateammonium salt (APFO). The oxygen free vessel was then heated up to 31°C. and the agitation system was set to 210 rpm. The vessel was chargedwith 165 g dimethylether and 4045 g hexafluoropropylene (HFP) to apressure of 7.91 bar absolute, with 187 g ethylene to 9.71 bar absoluteand with 2670 g tetrafluoroethylene (TFE) to 16.0 bar absolute reactionpressure. The polymerization was initiated by 70 ml of a 3.2% aqueouspotassium permanganate solution. As the reaction starts, the reactionpressure of 16.0 bar absolute was maintained by feeding TFE, ethyleneand HFP into the gas phase with a feeding ratio ethylene (kg)/TFE (kg)of 0.253 and HFP (kg)/TFE (kg) of 0.304. During polymerization a 3.2%aqueous potassium permanganate solution was continuously charged intothe vessel with a feeding rate 160 ml/h. The reaction temperature of 31°C. was also maintained.

Liquid dispersion samples were taken from the running polymerization at2.73 kg, 5.46 kg, 8.19 kg, 10.92 kg, 13.65 kg and 16.38 kg TFE monomerfeed. After feeding 19.16 kg TFE (405 min polymerization time), themonomer feed was interrupted and the monomer valves were closed. Thenthe reactor was vented and flushed with N₂ in three cycles.

The thus obtained 144.5 kg polymer dispersion with a solid content of20.2% consisted of latex particles having 64 nm in diameter according todynamic light scattering. The dispersion is recovered at the bottom ofthe reactor and worked up in analogy to Example 1 (this material isdesignated as “Example 6a” in the following). The same was done for theliquid dispersion samples that were taken from the runningpolymerization. All agglomerates were dried at 170° C. at vacuum for 16h. The MFI(265/5) and the melting points of the samples are reported inTable 5. As can be seen from table 5, the polymerization usingdimethylether as chain transfer agent only showed a marginal MFI driftof the polymer generated during the polymerization process.

TABLE 5 Analytical data of samples from polymerization of Example 6aSample taken at kg TFE feed MFI(265/5) [g/10 min] Tm [° C.]  2.73 8.9209.0  5.46 8.5 210.0  8.19 9.4 210.5 10.92 10.1 211.2 13.65 9.6 210.316.38 10.6 209.6 19.16 (final sample) 10.8 209.4

A comparative polymerization (herein referred as “Example 6b”) wascarried out under similar conditions as example 6a with the exceptionthat 72 g diethylmalonate (DEM) was used as chain transfer agent insteadof dimethylether. Liquid dispersion samples were also taken from thispolymerization, the reaction took 430 minutes. The work-up of thesamples as well as the drying conditions were the same as for Example6a, the analytical data of the samples are reported in Table 6.

TABLE 6 Analytical data of samples from polymerization of Example 6bSample taken at kg TFE feed MFI(265/5) [g/10 min] Tm [° C.]  2.73 295211.3  5.46 135 211.0  8.19 64 211.1 10.92 28 209.7 13.65 16.6 208.016.38 10.4 207.4 19.16 (final sample) 8.3 207.8

In comparison to example 6a, this polymerization using diethylmalonateas chain transfer agent showed a significant MFI drift of the polymerduring the polymerization process. If the MFI values of Table 6 areplotted versus the TFE monomer feed, a MFI value in the order of 500g/10 min can be extrapolated for the polymer material that is generatedin the first 5% of the monomer feed. This corresponds to a low molecularweight fraction of about 5%. This low molecular weight fraction is notpresent in the polymer of example 6a.

This finding was further confirmed by an extraction analysis carried outon the samples as follows: 100 g dried agglomerate of theTFE/HFP/ethylene-terpolymer sample of Example 6a was placed into aSoxhlet extraction apparatus, a glass cylinder bearing a glass frit inthe bottom was used as the sample holder. The polymer was extracted for5 days with acetone, the total extraction period was 33 h. After thisextraction period, the acetone was fully removed in a rotationevaporator under reduced pressure. 0.34 g of the dried residual remainedin the glass flask. 26% of this extractable was soluble in cold acetone,its solution viscosity in (MEK@35° C.) was 5 ml/g. The same extractionprocedure was carried out with polymer sample of Example 6b yielding anextraction amount of 2.32 g. 22% of this extractable was soluble in coldacetone. Indicative for a very low molecular weight, its solutionviscosity in (MEK@35° C.) was 7 ml/g.

From the soluble extractable fraction of Example 6b, some vapor pressuredata were recorded via a distillation under reduced pressure usingstandard lab equipment. The material was placed into a small glass tube(10 ml volume) equipped with a PTFE needle value and a mercurythermometer and connected to a standard mercury manometer with U tubegeometry. The glass tube was vented to 16 mbar and subsequently heatedup with a hot oil bath until the evaporation of the extractableoccurred. Under reflux conditions the approximate equilibriumtemperature was recorded. With this method, the equilibrium vaportemperature was measured at different predefined pressures (adjustableat the PTFE needle value). After measuring the vapor pressure at 240° C.the material was thermally degraded as could be seen by a darkdiscoloration of the extractable. The vapor pressure data are summarizedin Table 7.

TABLE 7 Vapor pressure data of the extractable of Example 6b T [° C.] p[mbar] 160 16 168 26 190 56 205 68 215 90 223 100  240 132 

The vapor pressure data of Table 7 plotted in an Arrhenius plot (In{p}versus 1/T) yields the enthalpy of evaporation of the low M_(w)extractable to be ΔH_(evap)=47.2 kJ/mol. A linear extrapolation of thesevapor pressure data to 297° C. yields a vapor pressure p=450 mbar at297° C. This analysis shows that the low molecular weight extractablefraction in example 6b has a vapor pressure nearly in the order of thenormal pressure under usual processing temperatures of theTFE/HFP/ethylene-terpolymer. This has consequences for the thermalstability of the fluororesin as the following investigation showed:

The agglomerates of the TFE/HFP/ethylene terpolymer samples of Example6a & Example 6b were examined for their thermal stability in a standardmelt indexer. In deviation of DIN 53735, ISO 12086 and ASTM D- 1238, thepolymer melt was exposed to 297° C. for one hour, before 5 kg weight wasapplied. As the visual inspection of the extruded monofils showed, theMFI strand of Example 6a was not discolored and did not contain anybubbles, whereas the MFI strand of Example 6b was brown discolored andcontained many bubbles. This demonstrates, that the thermal stability offluoropolymers produced via the process of the invention is greatlyimproved compared to prior art polymers.

Example 7

As a comparative example to example 8, a prior art material as disclosedin U.S. Pat. Nos. 5,256,745 & 5,208,305 was prepared according to thefollowing procedure:

A fluoroelastomer was prepared in the form of a latex (,,Latex 1,,) byaqueous emulsion polymerization. A polymerization vessel with a totalvolume of 47.5 l equipped with an impeller agitator system was chargedwith 29 l deionized water, 118.6 g hexamethyldisilane (chain transferagent) and 80 g FC-128 fluorosurfactant (C₈F₁₇SO₂N(C₂H₅)CH₂COO⁻K⁺ saltof 3M Company). The oxygen free vessel was then heated up to 71° C. andthe agitation system was set to 240 rpm. The vessel was charged withhexafluoropropylene (HFP) to 4.34 bar absolute, with vinylidenefluoride(VDF) to 7.88 bar absolute and with tetrafluoroethylene (TFE) to 9.5 barabsolute reaction pressure. The polymerization was initiated by theaddition of 109 g ammonium peroxodisulfate (APS) dissolved in water. Asthe reaction started, the reaction pressure of 9.5 bar absolute wasmaintained by feeding TFE, VDF and HFP into the gas phase with a feedingratio TFE (kg)/VDF (kg) of 0.705 and HFP (kg)/VDF (kg) of 1.185. Thereaction temperature of 71° C. was also maintained. After feeding 3.96kg VDF in a total reaction time of 6.5 hours, the monomer feed wasinterrupted and the monomer valves were closed. The reactor was ventedand flushed with N₂ in three cycles. The thus obtained 40.4 kg polymerdispersion with a solid content of 28.3% was recovered at the bottom ofthe reactor, it consisted of latex particles having 92 nm in diameteraccording to dynamic light scattering. 100 ml of this polymer dispersionwas coagulated by adding it drop-wise to an aqueous MgCl₂ solution withagitation, after which it was de-watered and washed three times withdeionized water (60-70° C.). The polymer was dried overnight at 130° C.in an air circulating oven. The polymer had the appearance of a brownsyrup and showed a solution viscosity of 14 ml/g.

A second fluoroelastomer precursor was prepared in the form of a latex(“Latex 2”) by aqueous emulsion polymerization in the same reactor asfor the preparation of “Latex 1” using 29 l deionized water and 160 gFC-128 fluorosurfactant. No chain transfer agent was utilized in thispolymerization. After heating up the vessel to 71° C., setting theagitation system to 240 rpm and degazing and charging with nitrogen inthree cycles, the vessel was charged with hexafluoropropylene (HFP) to4.21 bar absolute, with vinylidenefluoride (VDF) to 7.34 bar absoluteand with tetrafluoroethylene (TFE) to 8.8 bar absolute reactionpressure. The polymerization was initiated by the addition of 21 gammonium peroxodisulfate (APS) dissolved in water. As the reactionstarted, reaction temperature of 71° C. as well as the reaction pressureof 8.8 bar absolute was maintained by feeding TFE, VDF and HFP into thegas phase with a feeding ratio TFE (kg)/VDF (kg) of 0.705 and HFP(kg)/VDF (kg) of 1.185. After feeding 3.96 kg VDF in a total reactiontime of 8.0 hours, the monomer feed was interrupted and the monomervalves were closed. The reactor was vented and flushed with N₂ in threecycles. The thus obtained 40.3 kg polymer dispersion with a solidcontent of 28.2% was recovered at the bottom of the reactor and 85 g ofwet coagulate was removed from the dispersion via filtration of thedispersion through a filter with 80 μm mesh size. The dispersionconsisted of latex particles having 104 nm in diameter according todynamic light scattering. 100 ml of this polymer dispersion was workedup the same way as Latex 1, the raw polymer had a nearly whiteappearance and showed a solution viscosity of 108 ml/g.

Latex 1 and Latex 2 were blended undiluted such that the solid polymerswere in the ratio of 50:50 by weight. The latex was coagulated by addingit drop-wise to an aqueous MgCl₂ solution with agitation, after which itwas de-watered and washed three times with deionised water (60-70° C.).The polymer was dried overnight at 130° C. in an air circulating oven.The raw polymer had a slightly discolored appearance and showed asolution viscosity of 59 ml/g. As shown by size exclusion chromatography(SEC), the polymer exhibited a distinct bimodal molecular weightdistribution (MWD): The separate peak at low molecular weights had amass average molecular weight of M_(w)=10.700 g/mol, a polydispersity ofM_(w)/M_(n)=2.2 and an area of 55% of the total MWD. The separate peakat high molecular weights had a mass average molecular weight ofM_(w)=200.000 g/mol, a polydispersity of M_(w)/M_(n)=1.9 and an area of45% of the total MWD. The overall polydispersity of the sample wasM_(w)/M_(n)=11.2.

Example 8

A polymerization vessel with a total volume of 47.5 l equipped with animpeller agitator system was charged with 29 l deionized water, 1.3 gsodiumdisulfite (Na₂S₂O₅), 84 g perfluorooctanoate ammonium salt (APFO).The oxygen free vessel was then heated up to 70° C. and the agitationsystem was set to 240 rpm. The vessel was charged with 1.4 g methyltertiary butyl ether (MTBE) and with hexafluoropropylene (HFP) to 10.18bar absolute (1192 g), with vinylidenefluoride (VDF) to 13.52 barabsolute (175 g) and with tetrafluoroethylene (TFE) to 15.5 bar absolute(184 g) reaction pressure. The polymerization was initiated by theaddition of 40 g ammonium peroxodisulfate (APS) dissolved in water. Asthe reaction starts, the reaction pressure of 15.5 bar absolute wasmaintained by feeding TFE, VDF and HFP into the gas phase with a feedingratio TFE (kg)/VDF (kg) of 0.705 and HFP (kg)/VDF (kg) of 1.185. Thereaction temperature of 70° C. was also maintained.

After feeding 2.51 kg VDF (corresponds to 50% monomer target feed after65 min polymerization time), a portion of 68 g MTBE chain transfer agentwas added into the vessel which resulted in a drastic declination of themonomer uptake. The monomer feed was maintained for anotherpolymerization period of 200 min, until the monomer feed 5.01 kg VDF wascompleted. The monomer feed was interrupted and the monomer valves wereclosed. Within 10 min, the monomer gas phase was reacted down to avessel pressure of 8.6 bar; then the reactor was vented and flushed withN₂ in three cycles.

The thus obtained 43.5 kg polymer dispersion with a solid content of33.3% was recovered at the bottom of the reactor, it consisted of latexparticles having 114 nm in diameter according to dynamic lightscattering.

5.0 l of this polymer dispersion was freeze coagulated over night in arefrigerator. After thawing the material, the thus obtained sponge-linkeraw polymer was washed five times with demineralized water, the polymerwas squeezed out and dried for 12 h in an oven at 130° C. The polymerwas transparent and did not show any sign of discoloration, it had aMFI(265/5) of 12.5 g/10 min and a solution viscosity of 69 ml/g. Asdetermined by size exclusion chromatography (SEC), the polymer exhibiteda distinct bimodal molecular weight distribution (MWD): The separatepeak at low molecular weights had a mass average molecular weight ofM_(w)=13.300 g/mol, a polydispersity of M_(w)/M_(n)=2.2 and an area of54% of the total MWD. The separate peak at high molecular weights had amass average molecular weight of M_(w)=276.000 g/mol, a polydispersityof M_(w)/M_(n)=1.9 and an area of 46% of the total MWD. The overallpolydispersity of the sample was M_(w)/M_(n)=12.2.

100 parts of the polymer were mixed on a two roll mill with thefollowing ingredients:

5.95 (mmhr) Bisphenol AF

0.54 (mmhr) of the following phosphonium complex

(C₄H₉)₃P⁺CH₂CH(CH₃)OCH₃ ⁻OC₆H₄C(CF₃)₂C₆H₄OH

 which is tributylmethoxy propyl phosphonium chloride prepared fromtributyl phosphene (available from Cytec) allylchloride and methanol andthen reacting with the sodium salt of Bisphenol AF.

1.03 (mmhr) of a further complex which is a complex prepared by reactingtributylmethoxy propyl phosphonium chloride with the sodium salt ofperfluoroctyl-n-methylsulfonamide.

After measuring the Mooney viscosity of the curative blend (“ML1+10@121° C. incorporated cure”), the following other compoundingingredients were added: 3 g per hundred gram (phr) magnesium oxide(Elastomag 170 from Morton International) and 6 phr calcium hydroxideand 13 phr carbon black (N762). The composition was prepared in the formof individual sheets measuring 76×152×2 mm by pressing at 5-7 MPa at163° C. for 50 min. The same curing procedure was conducted on the priorart polymer sample described in example 7. Finally, both cured compoundswere tested and compared for various properties according to the testmethods set forth above. The test results are reported in Table 8.

TABLE 8 comparative Example 7 Example 8 MFI(265/5), raw gum [g/10 min]17.9 12.5 solution viscosity, MEK @ 35° C. [ml/g] 56 69 M_(w)/M_(n) (SECmeasurement) 11.2 12.2 ML 1 + 10 @ 121° C. incorporated cure 31 34 ML1 + 10 @ 121° C. compound 57 58 Physical properties of press cured sheetDurometer, shore A 68 64 Peak Stress [Mpa] 9.9 11.0 Peak Strain % 295235 100% Modulus [MPa] 2.8 3.2 Processing Evaluation (MPT), 105° C. Zone1, 180 s⁻¹ [MPa] 23.4 21.2 Zone 2, 361 s⁻¹ [MPa] 25.5 24.0 Zone 3, 723s⁻¹ [MPa] 28.2 26.6 Zone 4, 1446 s⁻¹ [MPa] 32.7 30.1 ProcessingEvaluation (MPT), 120° C. Zone 1, 180 s⁻¹ [MPa] 19.2 19.9 Zone 2, 361s⁻¹ [MPa] 21.7 21.6 Zone 3, 723 s⁻¹ [MPa] 24.5 23.9 Zone 4, 1446 s⁻¹[MPa] 28.1 26.5 Compression set of, cured sheet [%] 19 6 Wt %Extractables 13.6 5.7 Permeation,CM14 @ 40° C. [g · mm/m² · d] 55 51

This example demonstrates that the bimodal molecular weight distributionof the prior art material described in Example 7 can be generated inonly one single-step polymerization using a very effective and easy tohandle dialkylether as chain transfer agent. The polymerization of thebimodal single-step process is faster than each precursor polymerizationdescribed in Example 7.

Furthermore, any blending procedure involved in the polymer workup isavoided. Compared to the polymer of example 7, the fluoroelastomerprepared with the process of the invention showed a unique combinationof better processing characteristics (see processing evaluation),together with better mechanical data (see compression set), a lowervapor transmission (permeation) and a reduced extractable levels.

Example 9

A polymerization vessel with a total volume of 186.1 l equipped with animpeller agitator system was charged with 114.6 l deionized water, 8 goxalic acid, 47 g ammonium oxalate and 298 g perfluorooctanoate ammoniumsalt (APFO). In three subsequent cycles, the vessel was degassed andsubsequently charged with nitrogen to assure that all oxygen had beenremoved. The vessel was then heated up to 60° C. and the agitationsystem was set to 210 rpm. The vessel was charged with 132 gdimethylether (Me₂O) and 2472 g hexafluoropropylene (HFP) to a pressureof 5.84 bar absolute, with 1305 g vinylidenefluoride (VDF) to 12.18 barabsolute and with 1143 g tetrafluoroethylene (TFE) to 15.5 bar absolutereaction pressure. The polymerization was initiated by 55 ml of a 2.4%aqueous potassium permanganate solution. As the reaction started, thereaction pressure of 15.5 bar absolute was maintained by feeding TFE,VDF and HFP into the gas phase with a feeding ratio VDF (kg)/TFE (kg) of1.219 and HFP (kg)/TFE (kg) of 0.484. Within the polymerization, the2.4% aqueous potassium permanganate solution was continuously chargedinto the vessel with a feeding rate of 120 ml/h. A reaction temperatureof 60° C. was maintained.

After feeding 21.8 kg TFE (220 min polymerization time), the monomerfeed was interrupted and the monomer valves were closed, but theaddition of potassium permanganate solution was maintained at a feedrate of 40 ml/h. Within 10 min, the monomer gas phase was reacted downto a vessel pressure of 9.7 bar; then the reactor was vented and flushedwith N₂ in three cycles.

The thus obtained 173.4 kg polymer dispersion consisted of latexparticles having 118 nm in diameter according to dynamic lightscattering.

This polymer dispersion having a solid content of 33.8% was recovered atthe bottom of the reactor, passed through a glass column containingDOWEX 650C cation exchange resin (Dow Chemical Co.) and subsequentlytransferred into a 250-l agglomeration vessel. To the polymer dispersionwas added 100 l deionized water, 2.5 l concentrated hydrochloric acidand 35 l perfluoro n-heptane agglomeration aid (PF 5070 by 3M). Theagglomeration vessel was agitated vigorously until the solid has fullyseparated from the aqueous phase. The agglomerate was washed three timeswith deionized water, the agglomeration aid was distilled off and thepolymer was dried in an oven at 70° C. for 24 hours. The thus obtained58 kg polymer showed a melting point maximum of 100° C., the meltviscosity was MFI(265/5) 151 g/10 min. The MFI strand was translucentand showed no sign of discoloration and no bubbles. As shown by sizeexclusion chromatography (SEC), the polymer had a unimodal, symmetricalGaussian shaped molecular weight distribution (MWD) with a mass averagemolecular weight of M_(w)=49.300 g/mol and a polydispersity ofM_(w)/M_(n)=1.69. For this polymer, the solution viscosity of a 40%polymer solution in N,N′-dimethylacetamide was measured at differenttemperatures. These data are summarized in table 9.

TABLE 9 shear rate □@20° C. □@50° C. □@70° C. □@85° C. [1/s] [Pa · s][Pa · s] [Pa · s] [Pa · s] 18.5 18.8 6.55 3.62 2.50 23.2 19.1 6.58 3.652.52 29.2 19.3 6.59 3.65 2.52 36.7 — 6.61 3.66 2.53 46.0 — 6.65 3.682.54 58.1 — 6.66 3.69 2.54 73.0 — 6.68 3.71 2.55 91.9 — 6.69 3.72 2.56116 — — 3.75 2.57 146 — — 3.77 2.58

A polymerisation conducted under the same conditions but using 120 g ofmethoxy-2H-perfluorisobutylene (methanol adduct of perfluorisobutylene;a typical chain transfer agent for the semifluorinated componentsdisclosed in WO 00/32655) instead of 132 g dimethylether was completedin 150 min reaction time. The so-obtained resin had a melt viscosity toohigh to be determined by means of a standard melt index instrument—evenwith a load of 21.6 kg the MFI (265/21.6) was 0 g/10′.

This example demonstrates the preparation of translucent and highlysoluble fluoropolymers using the aqueous emulsion polymerization processwith dialkylethers as chain transfer agents. Because of the high chaintransfer activity of the dialkylethers, also low molecular weightpolymers can be made while maintaining a good productivity of thepolymerization process (high solid content in short reaction times). At265° C. processing temperatures, these polymers are thermally stable anddo not undergo thermal degradation which would result in discoloration.Because of the low molecular weights, even highly concentrated polymersolutions have a low viscosity. Therefore, the polymers made with theprocess of the invention can be used for any solution coatingapplication of fluoropolymers involving e.g. as cladding material forpolymer optical fibers (POF), as coating material of translucent fabricsor as primer material for fluoropolymers to other substrates (e.g. toglass surfaces).

Example 10

A polymerization vessel with a total volume of 186.1 l equipped with animpeller agitator system was charged with 114.6 l deionized water, 5 gsodium disulfite (Na₂S₂O₅) 298 g perfluorooctanoate ammonium salt(APFO). In three subsequent cycles, the vessel was degassed andsubsequently charged with nitrogen to assure that all oxygen had beenremoved. The vessel was then heated up to 70° C. and the agitationsystem was set to 210 rpm. The vessel was charged with 60 gdimethylether (Me₂O) and 2241 g hexafluoropropylene (HFP) to a pressureof 6.0 bar absolute and with 1882 g vinylidenefluoride (VDF) to 15.5 barabsolute reaction pressure. The polymerization was initiated by theaddition of 160 ml 30% aqueous ammonium peroxodisulfate (APS) solution.As the reaction started, the reaction pressure of 15.5 bar absolute wasmaintained by the feeding VDF and HFP into the gas phase with a feedingratio HFP (kg)/VDF (kg) of 0.632. After feeding 17.65 kg VDF, the HFPvalve was closed and only VDF was fed. When a total feed of 23.15 kg VDFwas reached, the HFP valve was opened again and the pressure wasmaintained by the feeding VDF and HFP with a feeding ratio of HFP(kg)/VDF (kg)=0.204.

When a VDF feed of 43.81 kg was reached in 250 min polymerization time,the monomer feed was interrupted and the monomer valves were closed.Within 15 minutes, the monomer gas phase was reacted down to a vesselpressure of 4.8 bar. Then the reactor was vented and flushed with N₂ inthree cycles.

The thus obtained 173.8 kg polymer dispersion with a solid content of34.4% was recovered at the bottom of the reactor and transferred into a250-l agglomeration vessel. The further workup of the polymer wascarried out the same way as for Example 8. The thus obtained 59 kgpolymer is a free flowing agglomerate. This material shows a meltingpoint maximum of 113° C. and a heat of fusion of 4.3 J/g, the meltviscosity is MFI(265/5) 7.6 g/10 min.

On a polyolefin blown mold film line, the performance of this particularmaterial was tested as a polymer melt processing additive. Thepolyolefin used for the test was the commercially available butenemodified linear low density polyethylene (LLDPE) grade Exxon 1001.32(MFI(190/2.16) of 1 g/10 min). A masterbatch of the fluoropolymer wascompounded to 3 wt % additive concentration in DFDA 7042 carrier resin(MFI(190/2.16) of 2 g/10 min). The blending with LLDPE was accomplishedby tumble blending the base resin with the masterbatch prior toextrusion, the thus obtained concentration of the fluoropolymer in theLLDPE was 750 ppm. The extrusion experiments were carried out on a 4.44m lab scale blown film line equipped with a 25 mm Collin twin screwextruder having a length/diameter ratio of 24/1, a 18/35/60 mesh screenpack, a 40 mm die with a 2 mm die gap and a single lip air ring. Theextruder output was 12.7 kg per hour, the temperature profile was thefollowing:

zone 1: 170° C. zone 2: 175° C. zone 3: 185° C. zone 4: 195° C. die:200° C.

The efficiency of the fluoropolymer was assessed by the reduction of thegate pressure and by the time required to completely eliminate the meltfracture during blown film extrusion of the LLDPE. Further on, theperformance of the fluoropolymer of this example to eliminate the meltfracture was compared to a VDF/HFP-copolymer as disclosed in U.S. Pat.Nos. 5,106,911, 5,464,904 and 5,710,217 (see comparative example intable 10). The results are summarized in Table 10.

TABLE 10 Example 9 comp. example initial gate pressure [PSI] 4750 4650time for complete melt 40 45 facture elimination [min] gate pressure(melt facture 3600 3650 100% eliminated) [PSI] ΔP [%] 24.2 21.5

This example demonstrates that the fluorinated copolymer produced viathe process of the invention is more efficient as the prior art polymerprocessing additive, because a larger extrusion pressure drop in ashorter processing time is provided. Further, this example has theadditional advantage that it is a free flowing material whichsignificantly simplifies the handling of the fluorinated copolymer aswell as the preparation of masterbatches of the processing aid.

What is claimed is:
 1. Method of making a fluoropolymer comprisingrepeating units derived from one or more gaseous fluorinated monomers,said method comprising an aqueous emulsion polymerization of saidgaseous fluorinated monomers in the presence of an ether selected fromthe group consisting of dimethyl ether (DME), methyl tertiary butylether (MTBE) and mixtures thereof.
 2. Method according to claim 1wherein said fluoropolymer has a partially fluorinated backbone. 3.Method according to claim 1 wherein said aqueous emulsion polymerizationinvolves a copolymerization of a gaseous fluorinated monomer selectedfrom the group consisting of tetrafluoroethylene,chlorotrifluoroethylene and vinylidene fluoride and a comonomer selectedfrom the group consisting of vinylidene fluoride, perfluoroalkyl vinylmonomers, fluorinated allyl ethers, fluorinated vinyl ethers, ethyleneand propylene.
 4. Method according to claim 3 wherein said fluorinatedvinyl ether is a perfluorovinyl ether of the formula: CF₂═CF—O—R_(f)wherein R_(f) represents a perfluorinated aliphatic group that maycontain one or more oxygen atoms.
 5. Method according to claim 1 whereinsaid aqueous emulsion polymerization is carried out in the presence of afluorinated surfactant.
 6. Method according to claim 3 wherein saidsurfactant is non-telogenic.
 7. Method according to claim 1 wherein saidfluoropolymer is a semi-crystalline fluoropolymer or an amorphousfluoropolymer.
 8. Method according to claim 1 wherein the fluoropolymerproduced is a copolymer selected from the group consisting of acopolymer of chlorotrifluoroethylene and vinylidene fluoride, acopolymer of tetrafluoroethylene and vinylidene fluoride, a copolymer ofvinylidene fluoride and hexafluoropropylene, a copolymer oftetrafluoroethylene and ethylene, a copolymer of tetrafluoroethylene andpropylene, a copolymer of vinylidene fluoride and a perfluorovinylether.
 9. Method according to claim 1 wherein said fluoropolymerproduced is a copolymer of tetrafluoroethylene, vinylidene fluoride andhexafluoropropylene, a copolymer of vinylidene fluoride,tetrafluoroethylene and a perfluorovinyl ether, a copolymer oftetrafluoroethylene, ethylene and hexafluoropropylene, a copolymer oftetrafluoroethylene, ethylene or propylene and a perfluorovinyl ether.10. Method according to claim 1 wherein said fluoropolymer produced is acopolymer of tetrafluoroethylene, ethylene or propylene,hexafluoropropylene and a perfluorovinyl ether.
 11. Method according toclaim 1 wherein said fluoropolymer is a curable fluoroelastomercomprising one or more cure site components.
 12. Method according toclaim 1 wherein said fluoropolymer is a fluorothermoplast having amelting point between 60° C. and 300° C.
 13. Method according to claim 1wherein said aqueous emulsion polymerization is carried out withoutadding a surfactant to the polymerization system.
 14. Method accordingto claim 13 wherein said polymerization is carried out in the presenceof a free radical initiator system comprising a reducing agent and anoxidizing agent, said free radical initiator system being added to theaqueous phase to initiate the aqueous emulsion polymerization andfurther reducing agent or oxidizing agent being added to the aqueousphase during the aqueous emulsion polymerization.
 15. Method accordingto claim 1 wherein the polymerization is conducted in such a way so asto produce a multi-modal molecular weight distribution.
 16. Methodaccording to claim 15 wherein said polymerization is a single steppolymerization.
 17. Method according to claim 15 wherein saidmulti-modal molecular weight distribution is obtained by adding no or aninitial charge of said ether at the beginning of the polymerization andone or more further charges during the polymerization.
 18. Methodaccording to claim 1 wherein a core shell polymer is produced. 19.Method according to claim 18 wherein the core is amorphous and the shellis semi-crystalline.
 20. Method of making a fluoropolymer comprisingrepeating units derived from one or more gaseous fluorinated monomers,said method comprising an aqueous emulsion polymerization of saidgaseous fluorinated monomers in the presence of an ether selected fromthe group consisting of dimethyl ether (DME), methyl tertiary butylether (MTBE) and mixtures thereof, wherein said fluoropolymer has apartially fluorinated backbone.